In the United States, all adult patients with a history of anaphylaxis on insect sting and a positive venom skin teat are treated with whole body extracts. We have shown that, contrary to this standard treatment for insect sting allergy, venom immunotherapy is effective. Recently, investigators in Holland have found that if they sting history-positive skin test-positive patients, more than 70% have no reaction, and, they contend, need no therapy. Incomplete US studies found fewer non-reactors on challenge sting. Neither the US nor the Dutch investigators have been able to develop diagnostic parameters to predict which patients will react to stings and which will not. The current proposal is based on the hypothesis that the European studies are, in part, correct and that it is unnecessary to treat as many patients as we do now. We will repeat their work, focusing on patients with milder reactions, and address a flaw in that study: the question of whether a single sting predicts the reaction to subsequent stings. We also hypothesize that clinical protection from allergen immunotherapy results from a mechanism of immunization unrelated to IgG blocking antibodies. Immunotherapy with allergen peptides leads to a lesser immediate allergic response on re-exposure to allergen. We will immunize patients with peptides from antigen 5, the major yellow jacket venom allergen. Standard immunotherpay with venom proteins leads to frequent large local reactions and, less often, to systemic anaphylaxis. Peptide immunotherapy does not cause any immediate reactions, but there is often a delayed and mild "anaphylactic-like" response which we believe is due to the generation of an HRF-like cytokine. We have developed a detailed protocol to ascertain the nature of this response. Finally, the major goal of these studies is to use the stings of a hundred or more patients to develop parameters which predict which individuals will have a reaction to a sting. In the current work, we plan to study not only immunoglobulin levels but inflammatory cell activation, cytokine production, blood and urine histamine levels and tryptase levels. Further, based on the results of earlier studies, we will also study the state of activation of the kinin coagulation pathways. Venom immunotherapy (VIT) is recommended based on perceived high risk (>50%) of future systemic reaction (SR), fear of worsening SR and lack of a specific prognostic test. This sting challenge program seeks to define clinical and laboratory characteristics associated with lower risk of SR in patients with SR history and positive venom skin tests (VST). Insect stings were performed in a monitored clinical setting and patients were observed for objective signs and subjective symptoms of SR. Of 350 patients who reported "severe" sting reactions, sting challenge was performed on 52 patients: mean age 45 yrs, 34M, 18F. VST was positive to yellow jacket (YJ) in 52 patients and honeybee (HB) in 12 patients. The clinical history was classified as mild (14), moderate (20), moderate- severe (14) or questionable (4); patterns of previous SR included single (29) or multiple (23) reactions, sequential or multiple stings (19). The median time since the last SR was 2 years (range 0-24); it was over 10 years in 10 patients (5 in childhood). Sting challenge caused systemic symptoms in 9 patients (17%); 3 moderate-severe, 2 moderate, 4 mild. Another 7 had borderline reactions. No reaction was worse than the patient's previous SR. The frequency and severity of reaction was greater in patients with moderate-severe previous SR (36%) than in patients with mild-moderate previous SR (10%). The low reaction rate is most likely related to many of our patients having low risk (mild SR, remote SR, multiple/sequential stings). Still, each of these patients would almost certainly have been advised to receive VIT by an allergist. We conclude that there are clinical parameters that may distinguish patients with low risk of SR who could safely forego VIT. Many more patients need to be studied with supervised challenge to define accurately the contribution of the many clinical and immunologic factors involved in SR to insect stings.